Use the end date shown in your account
Number rentals use the period and expiry shown for that purchase. A calendar month is not always the same number of days. Check the actual end date rather than estimating it from a fixed day count.
Where renewal is available, arrange it before expiry and review the price and payment terms. An optional auto-renewal setting must be enabled and authorized; simply keeping a number in your inbox does not renew it.
After expiry, incoming access can stop and the number may become unavailable or later be reassigned. Do not assume that a delayed renewal can recover the same number.
Keep an independent account recovery method with any service where you use the number. Contact support promptly if a renewal is pending or the displayed end date seems wrong.